Fixing element for osteosynthesis

ABSTRACT

An osteosynthetical fixing element, for the fixing of a bone implant, includes an accommodating body which is adapted to be introduced into a bone bore-hole and an expanding body, where, as a result of the driving-in of the expanding body into a longitudinally directed opening having a continuous wall, the accommodating body is radially expandable by a wedge effect. The accommodating body is sub-divided in the longitudinal direction, and includes at least two sub-elements which form a shaft with a cavity and are separate from one another or are connected to one another so as to be moveable in such a manner that as a result of the driving-in of the expanding body into the cavity, the accommodating body is expandable, substantially over its entire length, as a result of the mutual wedge effect of the accommodating body and expanding body.

BACKGROUND OF THE INVENTION

The invention relates to an osteosynthetical fixing element for thefixing of a bone implant which bone bore-hole and an expanding bodywhich can be driven into an opening of the accommodating body and wherethe accommodating body is radially expandable by a wedge effect.

EP-B1 409 364 discloses a connecting element for osteosynthesis which isdesigned as an expandable, elastically deformable sleeve. The sleeve hasa diameter which, reduces from an end side and is provided with a slotextending in the longitudinal direction. The expansion of the sleeve iseffected by a pin which is designed so as to be axially symmetrical andpreferably tapers in conical fashion in the direction of insertion andwhose outer diameter is greater than the smallest outer diameter of thesleeve and smaller than the greatest outer diameter thereon. At theperiphery of the sleeve different kinds of toothing elements areprovided consisting for example of sawtooth-shaped barbs, helical orconcentric projections.

Upon the driving-in of the pin, the outer wall of the sleeve, insertedinto a corresponding bore in the bone fragments to be connected, ispressed against the surrounding bone material and wedged accordingly.

A disadvantage of the known implant for the osteosynthetic connection ofreset bone fragments consists, in particular, in that--independently ofthe quality of its stabilising effect--primarily the attainablestability of the connection is unpredictable and highly variable in thelongitudinal direction.

Furthermore, upon the fixing of this element torsion stresses arisewhich are unpredictable in terms of their effects and which reduce thestability of the connection.

SUMMARY OF THE INVENTION

Commencing from the shortcomings of the prior art, the object of theinvention is to provide a fixing element of the type referred to in theintroduction with which an improved osteosynthetic stabilisation,approximating the fixing properties of a metallic fixing element, isattainable.

This object is fulfilled by the instant invention where theaccommodating body is subdivided in the longitudinal direction andincludes at least two sub-elements which are separate from one anotheror are connected to one another so as to be movable in such a manner sothat the driving-in of the expanding body into the accommodating bodyresults in the accommodating body being expandable, substantially overits entire length, as a result of the mutual wedge effect of theaccommodating body and the expanding body.

The invention includes the recognition that, in the case of anosteosynthetic fixing element insertable in an accommodating opening(bore or other longitudinal channel), as uniform as possible anintroduction of force should take place for the attainment of a stableconnection to the bone. This relates both to the fixing of bonefragments and to the fixing of ligaments to the bone. The correspondingalso applies to the fixing of plates. In order to replace theconventionally used screw, an element is required which, solely byvirtue of its expansion, facilitates the introduction of force over theentire bone area which is passed through, without the stability of saidelement being subjected to excess stress. Therefore for exampleinsertion under torsion stress, as in the case of conventional metalscrews, is not to be employed.

In contrast to the known conical expanding element, it is provided thatthe relative expansion takes place over the entire length of the outersurface, which latter is in engagement with the bone material, and by asconstant as possible a longitudinal amount sufficient to establish areliable interlocking connection of the outer profiling. Thecross-sectional enlargement relates to that part of the individualsub-elements which is in the leading position during the insertion ofthe expanding body and thus forms the movement front. Here double tripleor also multiple subdivision in the longitudinal direction is possible.Due to the fact that the sub-elements are freely displaceable relativeto one another in the radial and tangential directions, in order to beinserted into a bore they are brought into a compressed position inwhich the wall of the bore has not yet been reached. Instead of bores ofcircular cross-section, longitudinal channels which have othercross-sectional shapes and/or which are tapered in the direction ofinsertion are also suitable.

Upon the expansion of the sub-elements (driven through the expandingbody which latter bears, as far possible, against the entire length ofthe inner opening and has uniform, ascending wedge-shaped surfaces), thesaid sub-elements execute a movement in the radial direction, where avertical line, which contacts the wall substantially over the entirelength, leads in the expansion movement and penetrates into the wall bythe full travel distance and over the full length. In the case of twosub-elements, these are two oppositely disposed outer zones, whereas inthe case of three sub-elements a structure is formed which resembles thejaws of a drill chuck. Here, however, in contrast to the latter, it isnot a question of an engaging action relative to an inner, cylindricaldrill but an engagement into the outer wall.

Thus in a preferred embodiment the outer curvature of the sub-elementsis to be selected such that it corresponds to the expandedcross-section. Since in this case the lateral lines of the sub-elementsinitially form a tangent with the bore, it can be favourable to causethe corresponding zone to reduce slightly in cross-section to enable aslarge as possible a fixing element to be introduced into a givenbore-hole and to make the relative expansion movement as large aspossible.

In the case of polygonal subdivision, the expanding body is to be of acorrespondingly polygonal formation, and a corresponding, similarsliding surface is to be provided for each outer sub-element.

When the fixing element according to the invention is used for thefixing of ligaments or the like in the bore-hole, the peripheralcross-section thereof preferably comprises a corresponding recess forthe clamping insertion of the corresponding element.

A peripheral, flange-like collar serves for the fixing of plates and thelike.

A particular advantage of the invention consists in that the expansiontakes place substantially uniformly over the entire length so that notorsional or rotating movements can arise which could result innon-uniform fixing with the risk of local excess stress.

It is also particularly favorable for the depth of the outer profilingto correspond to the attainable travel so that a compression zone withinthe structure is available to the displaced bone material.

In accordance with a preferred embodiment, the fixing element forosteosynthesis consists of a substantially rod-shaped accommodatingbody, comprising two sub-elements which define a cavity, and of anexpanding body. The accommodating body, positioned in a bone bore-holefor the connection of bone fragments, changes its spatial configurationwhen the expanding body enters the cavity, which latter is surrounded bythe sub-elements and extends over the entire length of the accommodatingbody. The sub-elements of the accommodating body are not permanentlyconnected to one another but are retained by guide elements in arelative position to one another such that upon the insertion of theexpanding body into the cavity, a uniform change occurs in the spacingbetween the respective sub-element and the longitudinal axis of theaccommodating body in a direction, in each case, at right angles to thisaxis.

In this way--as previously explained--advantageously it is obtained thatthe sub-elements are not subjected to deformation as a result of theexpansion process and a substantially uniform surface pressure isgenerated between the outer wall of the fixing element and the bonematerial over the entire length of the fixing element.

The guide elements are designed as a slide-guide comprising a tongue anda recess which receives the tongue, where the guide elements are in eachcase disposed on the mutually facing sides of the sub-elements and inactive engagement when the fixing element is inserted into a bonebore-hole.

The cavity present between the sub-elements of the accommodating bodyhas a quadrilateral, for example rectangular, cross-section which, inaccordance with an advantageous further development of the invention,enlarges in wedge-like formation on one side in an end zone in thedirection of the cavity opening. This substantially facilitates thedriving-in of an expanding body, having the form of a rod-shapedparallelepiped, during the surgical intervention. Theparallelepiped-shaped cross-section is adapted to the rectangularcross-sectional profile of the cavity in the accommodating body, wherehowever the lateral or vertical dimension has a greater value comparedto the cross-sectional profile of the cavity in order to obtain thedesired expansion effect. Furthermore, for the insertion of theexpanding body into the enlarging opening of the accommodating body itis favorable to taper the expanding body by the provision of awedge-shaped chamfer at the end which is be inserted.

The quadrilateral cross-section of the cavity and of the expanding body,in cooperation with the slide-guide, ensure that, upon the driving-in ofthe expanding body, a movement of the sub-elements of the accommodatingbody occurs where the said sub-elements retain their parallelism andtheir mirror-symmetrical position relative to the axis of the cavity.This facilitates a uniform movement of the sub-elements at right anglesto this longitudinal axis and in opposition to one another and bringsabout a substantially uniform surface pressure between the outer wall ofthe fixing element and the surrounding bone material over the entirelength of the fixing element.

In accordance with another embodiment of the invention, that end of theexpanding body which lies opposite the wedge-shaped end portioncomprises a profiled wall which forms an enlarged contact surface forthe temporary interlocking- and frictional fixing of a surgical toolprovided for easy handling of the expanding body. Profile sections oftriangular cross-section extending transversely to the longitudinal axisof the expanding body are particularly suitable for this purpose. Forthe handling of the expanding body it is equally important for theaccommodating body to possess a shorter length than the expanding body.This ensures that the profiled end of the expanding body is still ableto be handled when the expanding body has already completely penetratedthe accommodating body.

In accordance with another favorable further development of theinvention, the sub-elements of the accommodating body have the form oflongitudinal-section-halves of a hollow cylinder in each case comprisinga recess which, upon the assembly of the accommodating body, define asubstantially rectangular cavity. On the side on which the expandingbody is introduced, the sub-elements in each case bear a flange-likecollar which facilitates an accurate and secure positioning of theaccommodating body in the bore-hole provided in the bone parts to beconnected. In a simple manner, the collar likewise prevents theaccommodating body from not being pressed into the bore when theexpanding body is being driven in.

The interlocking fixing of the sub-elements of the accommodating body inthe bone material is achieved in a favourable manner by a profiledsurface of its outer wall. For this purpose grooves are provided whichare arranged in the form of a half-ring and which have a triangularcross-section. The number and/or shape of the grooves is selected suchthat a longitudinal section through the sub-elements has asawtooth-shaped boundary line.

In accordance with another further development of the invention, thesub-elements have a different cross-sectional profile. Here in the caseof one sub-element the periphery thereof is provided with a flattenedarea extending over the entire length. Advantageously, when anaccommodating body is inserted into the bone bore-hole this results inan additional free space between the respective walls, in which freespace a further element to be permanently attached to the bone can bepositioned. This feature of the invention provides, for example,favorable osteosynthetic conditions for a knee joint operation where,for the fixing of the cruciate ligament, a bone portion with grown-ontendon is inserted in such a free space and can be fixed by theexpansion of the accommodating body.

Both the accommodating body and the expanding body consist of a materialwhich, with acceptable biological compatibility, is subject to resorbingdecomposition and is produced by injection molding. A polylactide,polyglycolide or clockwise- or anticlockwise-rotatory copolymer of thesesubstances is preferably provided as the material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and advantageous further developments thereof and will beexplained in detail in the following together with the description ofthe preferred embodiment of the invention making reference to theFigures wherein:

FIG. 1 is a front view of the preferred embodiment of the invention inthe unexpanded state;

FIG. 1a is a lateral view from the right corresponding to theillustration in FIG. 1;

FIG. 2 is a front view of the preferred embodiment of the inventionfollowing the driving-in of an expanding body (not shown);

FIG. 2a is a lateral view from the right corresponding to theillustration in FIG. 2;

FIG. 3 is a lateral view of a favorable embodiment of an expanding bodyand

FIG. 4 is a plan view of a bone area with an inserted fixing element ina schematic illustration.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The accommodating body 1, illustrated in a front view and side view inFIGS. 1 and 1a respectively, is composed of two rod-shaped sub-elements2 and 3 of different formation comprising an equal-sized, axiallyextending, rectangular recess (compare items 9.2 and 9.3 in FIGS. 2 and2a). The sub-elements 2, 3 are not permanently connected to one another.They are retained in the illustrated position by guide elements (compareitems 4 and 5 in FIGS. 2 and 2a) and form a hollow-cylindrical bodywhich is flattened on one side. The recesses in the sub-elements 2, 3define a cavity 9 of rectangular cross-section which extends over theentire length of the accommodating body 1. One end zone of the cavity 9is provided with a wedge-shaped enlargement 11 in the direction of thecavity opening. This substantially simplifies the driving-in of anexpanding body in the form of an oblong parallelepiped (not shown,compare item, 20 in FIG. 3) during the surgical intervention.

As a result of the one-sided flattening 3.1 at the periphery of thesub-element 3, advantageously a free space is provided between theaccommodating body 1 inserted into a bone bore-hole and the wall of saidbore-hole, into which free space an additional element, to beosteosynthetically connected, can be introduced prior to the driving-inof the expanding body. This shape of the fixing element thus providesfavorable conditions for knee joint operations in which acruciate-ligament attachment is provided.

Each of the sub-elements 2, 3 bears a flange-like collar 6, 7, in eachcase at the same end. This collar ensures that an accommodating body 1,introduced into a bone bore-hole during an osteosynthetic intervention,remains in the desired position when the expanding body is inserted intothe cavity 9 along the axis 10.

When an accommodating body 1 has been inserted into a bore -hole, theprofiling provided at the periphery of the sub-elements 2, 3 results inthe fixing of said accommodating body and a favorable introduction offorce into the-bone when the expanding body is driven into the cavity 9.The profiling is formed by similar, triangular-shaped grooves 8 whichextend around the sub-elements in each case in the form of a half-ringand converge in peripheral edges 12.

The accommodating body 1 shown in FIGS. 2 and 2a is enlarged in itsspatial configuration by an expanding body (not shown) driven into thecavity 9. Here the sub-elements 2, 3 have been displaced in oppositedirections and in each case by the same amount in a direction at rightangles to the cavity axis 10. This movement is brought about by theslide-guide, which latter comprises a tongue 5 and a rectangular recess4, and by the rectangular shape of the recesses 9.2, 9.3 defining thechannel 9 and of the rod-shaped expanding body, and ensures a uniformpressure by the profiled wall of the sub-elements 2, 3 against the bonematerial over the entire length of the fixing element.

The expanding body 20, illustrated in FIG. 3, of the fixing elementconsists, like the sub-elements of the accommodating body, of a materialwhich is subject to resorbing decomposition in the human body. Therod-shaped expanding body has a rectangular cross-sectional profile andat one of its ends 21 forms a wedge-shaped chamfer 21.1 whichsubstantially simplifies the insertion of the expanding body into anaccommodating body positioned in the bone material. At the other end 22profiling 22.1 is provided to enable a more secure positioning of a toolfor the handling of the expanding body during an osteosyntheticintervention. The profiling consists of ribs of triangular cross-sectionwhich extend transversely to the longitudinal axis of the expandingbody.

The bone area 23 illustrated in FIG. 4 comprises a bore-hole 23.1 intowhich the accommodating body, comprising the sub-elements 2 and 3, isinserted. Due to the flattening at the periphery of sub-element 3, afree space remains between the wall of the bore-hole and theaccommodating body. This free space can be utilized for the insertion ofelements 24, 25 to be attached during an osteosynthetic intervention.Thus for example in the case of a knee joint operation withcruciate-ligament replacement, the free space provides favorableconditions for the positioning of a bone portion with tendon 25 attachedthereto. Following the driving-in of the expanding body (not shown),bone portion 24 and tendon 25 elements of the sub-element 3 are pressedagainst the wall of the bone in a fixing manner.

The invention is not limited to the preferred exemplary embodimentdescribed in the foregoing. Rather, a number of variants are conceivablewhich also apply the described invention in basically different types ofembodiments.

I claim:
 1. An osteosynthetical fixing element, for the fixing of a boneimplant, comprising an accommodating body made from a bioresorbablematerial which is adapted to be introduced into a bone bore-hole and anexpanding body, where, as a result of the driving-in of the expandingbody into a longitudinally directed opening having a continuous wall,the accommodating body is radially expandable by a wedge effect, whereinthe accommodating body, sub-divided in the longitudinal direction,comprises at least two sub-elements which form a shaft with a cavity andare separate from one another or are connected to one another so as tobe moveable in such a manner that as a result of the driving-in of theexpanding body into the cavity, the accommodating body is uniformlyradially expandable, substantially over its entire length, as a resultof the mutual wedge effect of the accommodating body and expanding body.2. A fixing element according to claim 1, wherein the cavity formed bythe at least two sub-elements is cylindrical on one side and has asubstantially polygonal cross-section on the other side.
 3. A fixingelement according to claim 1, wherein the at least two sub-elementscomplement one another to form a body having a substantially cylindricalouter wall of uniform cross-section.
 4. A fixing element according toclaim 3, wherein in the outer peripheral area, at least over a part oftheir longitudinal extent, the at least two sub-elements compriseprofiling or structuring which extends substantially transversely to thedirection of insertion of the fixing element into the bone and theprofiling consists of grooves of triangular cross-section which engagearound the sub-elements substantially in the form of a half-ring.
 5. Afixing element according to claim 1, wherein at least two of thesub-elements have different cross-sectional shapes in the shaft area. 6.A fixing element according to claim 5, wherein at least one sub-elementcomprises an outer flattening of its outer curvature extending over atleast a part of the length of the shaft.
 7. A fixing element accordingto claim 1, wherein at least one of the sub-elements is provided with aflange-like collar.
 8. A fixing element according to claim 1, furtherincluding an engaging element in the form of a tangentially extendingtongue, said engagement element being provided on one of thesub-elements or a corresponding engaging element and being designed forengagement into a recess provided in the other sub-element for theguiding accommodation of the tongue.
 9. A fixing element according toclaim 1, wherein the cavity enlarges slightly in wedge-shaped formationtowards that end of the sub-element which bears a flange-like collar.10. A fixing element according to claim 1, wherein the end of theexpanding body which has a smaller cross-section comprises asubstantially wedge-shaped chamfer and/or the length of the expandingbody exceeds the length of the sub-elements.
 11. A fixing elementaccording to claim 10, wherein the end of the expanding body which is atthe rear upon insertion comprises profiling to improve the engagement ofa tool.
 12. A fixing element according to claim 11, wherein theprofiling is provided on two side surfaces arranged opposite one anotherand comprises profile elements, extending transversely to thelongitudinal axis of the expanding body, of preferably triangularcross-section.
 13. A fixing element according to claim 1, whereinpolylactide, polyglycolide or a clockwise- or anticlockwise-rotatorycopolymer of these substances is provided as resorbable material.